Evaporative coolers are well known in the art. In general, these coolers rely on the evaporation of water to lower the wet bulb temperature of an air stream. Traditional direct air evaporative cooling systems simply draw air through wetted, chemically treated filter pads. Movement of the air through the pads evaporates water and cools the air. In direct air evaporative coolers, this air is utilized as a primary air stream for air conditioning and other applications. Such direct air evaporative cooling systems are most efficient in conditions of low humidity.
Indirect evaporative cooling systems combine the evaporative cooling effect in a secondary air stream. A heat exchanger is utilized to produce cooling in the primary air stream without the addition of moisture. In general, an indirect or dry evaporative cooler may include tubes containing flowing warm air on the inside, which is to be cooled by falling water on the outside of the tubes. A secondary scavenger air stream may also be included for contact with the falling water for removal of heat by evaporation. This secondary air stream may then be demoisturized and exhausted.
Indirect evaporative coolers have been proven in the art as able to cool buildings at one-third the electrical power demand of refrigeration units. This produces two-thirds less effluents from coal, oil, and gas fired power plants and helps to reduce various atmospheric pollutants. Carbon dioxide effluents contributing to the greenhouse effect, sulphur dioxide effluents contributing to acid rain, and nitrous oxides effluents contributing to smog are all reduced. Additionally, chlorine-based refrigerants are not needed and degradation of the earth's ozone layer is reduced. Moreover, indirect coolers can be used to supply all outside air to buildings to remove indoor air pollutants such as smoke and odors.
Existing evaporative coolers of the dry or indirect type, however, do not presently hold a large share of the market for cooling of buildings. In competition with other types of cooling, there are the disadvantages of higher first cost, greater bulk, lower cooling efficiency, unsuitable methods for retaining water on the wet sides of the tubes, and increased maintenance costs.
The present invention is directed to an indirect evaporative cooling system with a novel heat exchanger which overcomes some of these prior art problems and provides an efficient, compact, and relatively inexpensive system.